In general, in a cleaning device used for an image forming apparatus, the major method has been that toner on an image bearing member is removed by continuously bringing a blade made of a material such as urethane rubber into close contact with the image bearing member. In this method, it has been known that foreign matter such as paper powder is caught at the pointed end of a blade whereby the lip of the blade or cleaning failure is caused. As a countermeasure against the problem, there is disclosed in Patent Documents 1 to 3 as shown below a method in which, to remove foreign matter from the pointed end of a blade, an image forming job being run is interrupted to stop the movement of an image bearing member or to rotate it in the reverse direction.
The image forming apparatus described in Japanese Patent Application Publication No. 2002-311771 is provided with a cleaning action of a blade in which a photoreceptor is rotated in the opposite direction to the direction at the time of image formation, and carries out the cleaning action at every prescribed interval of the number of image formation to make it possible to maintain excellent cleaning properties over a long period of time. The prescribed interval is selected based on the number of cartridges used or environmental conditions (temperature or humidity).
The image forming apparatus described in Japanese Patent Application Publication No. 2005-31431 has a cleaning action of a blade in which the apparatus controls a photoreceptor driving motor to stop the photoreceptor, rotate it in the reverse direction and then rotate it in the normal direction during job operations of continuous printing, and returns to the original continuous printing job, and thereby repeats the cleaning action of a blade in a unit of the number of prescribed printing to prevent accumulation of paper powder at an edge of the blade, and to decrease printing failure and improve reliability.
Further, in the image forming apparatus described in Japanese Patent Application Publication No. 2007-328088, a cleaning action of a blade is repeated in which the direction of rotation of the photoreceptor is reversed at every prescribed number of rotations in accordance with the number of rotations of the photoreceptor.
However, it was found that cleaning failure on the image bearing member cannot be sufficiently prevented, in the image forming apparatus comprising a cleaning means which cleans the surface of an image bearing member by bringing a cleaning blade into close contact with the image bearing member, and a transfer means which transfers electrostatically a toner image on the image bearing member onto a sheet of paper using a transfer member on which a bias voltage was applied and a lubricant was applied, even if the technology described in Patent Documents 1 to 3, that is, the cleaning action of a blade in which, to remove foreign matter such as paper powder from the blade, a printing job is interrupted during an operation of continuous printing job at every prescribed interval to stop an image bearing member or to rotate it in the reverse direction is carried out.
This problem is one in which, in the case where large size printing jobs are continually carried out after small size printing jobs were continually carried out, a cleaning failure occurs on both side areas in the main scanning direction of a large size sheet of paper before reaching the above prescribed interval, that is, before carrying out the cleaning action of the cleaning blade.
The object of the present invention is to provide an image forming apparatus capable of preventing cleaning failure which occurs on both side areas in the main scanning direction of a large size sheet of paper in the case where large size printing jobs are continually carried out after small size printing jobs were continually carried out.